This invention provides a means of connecting a casing head, or other attachment, to string of tubular body such as a casing pipe, and in addition provides a means of transferring a portion of the load of that attachment onto a conductor pipe or other tubular body.
The typical fashion in which a well is drilled in the ground, for example for oil and gas, is to first drive or drill a shallow large diameter pipe, commonly called the conductor pipe, into the ground and to then drill a smaller and deeper hole inside the boundary defined by the conductor pipe so that a smaller diameter and longer pipe, commonly called the surface casing or casing pipe, can be placed into the hole. The annular space between the surface casing and the conductor pipe is then be filled with cement. Further drilling beyond the depth of the surface casing is done to a sufficient depth that geological formations encountered may cause pressurized fluid to escape into the hole and travel the surface. To control this fluid, and to prevent its escape into the atmosphere, the drilling is done through a sealed pressure vessel at the surface that is known as the blowout preventer stack. In addition, drilling at these depths require the use of a weighted column of fluid, known as drilling mud, to control the well and to aid drilling by cooling the drilling bit and to remove cut rock. A pressure vessel known as the casing head, attaches to and seals on around the surface casing to provide a means of hooking up the blowout preventer stack and the drilling mud lines. This casing head is commonly attached to the surface casing by either threading it onto the casing pipe or by welding it to the casing pipe. The problems with these methods of attaching the casing head are that they require time, are often expensive and create the possibility of installation errors.
A third method is to attach the casing head using a means for gripping the casing pipe with mechanically activated teeth. A seal between the casing head and the casing pipe is then provided separately, usually in the form of an elastomeric or metal seal ring located in the casing head above the mechanical gripping mechanism. Such an assembly is well known in the industry and commonly used but is described adequately in U.S. Pat. No. 4,799,714 issued to Collet, U.S. Pat. No. 5,332,043 issued to Ferguson, and Canadian Patent 2,015,966 issued to Anderson et al. Each of these patents describes a common method for mechanically attaching the casing head to the surface casing. They disclose the use of conical slip segments which surround the casing pipe, each slip segment being provided with a plurality of grooves on their straight inside surface (casing pipe-contacting surface) that act as teeth that bite into the surface casing. A housing, or actuation sleeve, with a reverse conical mating surface to the conical surface on the outside of the slip segments, is then driven against the slip segments (or the slip segments are driven against the sleeve/housing). This forces the slip segments against the surface casing pipe causing the grooves to frictionally grip (or the teeth to bite into) the casing pipe, and thus to secure the casing pipe to the casing head. These slip segments are commonly referred to as xe2x80x9cslipsxe2x80x9d and the system is commonly described as a slip lock casing connector.
This slip lock casing connector has advantages over the previously described casing connectors. These include the reduced installation time, the ability to ensure that a seal between the casing pipe and the casing head has been achieved, and the ability to remove the casing head if drilling is abandoned.
Once the casing head has been attached, by any of the three means described above, drilling is continued to a deeper depth. An additional, smaller, string of pipe is then set in the hole and the weight of this pipe is supported by the casing head. Further drilling steps could include setting of additional strings of pipe within the casing pipe, and installing additional heads above the casing head. The weight from the additional strings and heads can prove to be too large for the surface casing string to support alone, so some means of transferring this load onto the conductor pipe may be required. The equipment that transfers this load is known as the landing base. The landing base usually consists of a landing plate set on top of the conductor pipe, together with a means for setting the casing head on, or securing the casing head to, this landing plate. It can be extremely difficult to supply a landing base with a casing head using a slip lock connector as described above because the landing base interferes with the operator""s access to the mechanical actuation means of the casing connector. In addition, the casing head normally requires a special means of attachment to the landing base, and as such, the landing base cannot be fitted onto a standard slip lock casing head. The solution to these problems often leads to an awkward and complex system that can be extremely costly.
Commonly, the mechanical actuation means of the slip lock casing connector consists of studs or bolts that pull the actuation sleeve against the slip segments or push the slip segments against the actuation sleeve. In order to reduce the size of the entire assembly, these bolts or studs normally extend out below the bottom of the casing head. The use of a landing base interferes with access to the bolts of the mechanical actuation means, which requires the bolts to extend out of the top face of the bottom casing head (i.e., upwards out of the top face of a flange on the bottom of the casing head). This in turn requires the casing connector parts to be larger so that the bolts or studs clear the outside diameter of the casing head leading to a redesign of the slip lock casing head and an increased cost.
An objective of this invention is to establish a mechanical means of attaching a casing head or other attachment onto a piece of surface casing pipe or other pipe. The invention allows a landing base to be easily attached to the casing head. This invention reduces manufacturing costs of this combined casing head and landing base when compared to other available designs. Preferably, the invention allows the operator to establish and adjust the portion of load transferred from the surface casing onto the conductor pipe. Finally, the invention is easy to use and less awkward then available designs.
Broadly stated, the invention provides a connector head for connecting an inner tubular body within an outer, concentric tubular body, and for transferring at least a portion of the load from the inner tubular body onto the outer tubular body. The connector head of the invention comprises:
a generally tubular connector head formed with a central bore through which the inner tubular body extends, the connector head having an inwardly extending stop shoulder formed in the central bore to allow the connector head to rest on the upper end of the inner tubular body;
slip connecting means in the connector head for gripping the outer wall of the inner tubular body;
a base plate formed with a central bore through which the inner tubular body extends, the base plate being located below the connector head and adapted to rest on the upper end of the outer tubular body, the base plate being formed with a plurality of radially spaced holes;
a plurality of threaded stud members connected to and extending radially downwardly from the lower end of the connector head, for mating arrangement with the radially spaced holes of the base plate;
a retainer ring formed with a central bore through which the inner tubular body extends, the retainer ring being located between the connector head and the base place, and being connected to or in contact with the slip connecting means such that upward movement of the retainer ring engages the slip connecting means into a gripping mode with the inner tubular body, the retainer ring being formed with a plurality of radially spaced holes through which the threaded stud members extend, allowing the retainer ring to slide upwardly and downwardly on the threaded stud members; and
an upper and lower nut threaded onto each of the threaded stud members between the retainer ring and the base plate, such that tightening of the upper nuts against the retainer ring pushes the retainer ring upwardly to engage the slip connecting means into the gripping mode with the inner tubular body, and downward tightening of the lower nuts against the base plate transfers at least a portion of the load from the inner tubular body through the threaded stud members and lower nuts onto the base plate and the outer tubular body.
In a preferred embodiment, the connector head of the invention is a casing head device for use in a well bore, wherein the inner tubular body is a casing pipe and wherein the outer tubular body is a conductor pipe. In this embodiment the invention provides a casing head device for connecting and sealing to a casing pipe and for transferring at least a portion of the load from the casing pipe to an outer, concentric conductor pipe.